Data Communications and Computer Networks Chapter 4 CS 3830 Lecture 18 Omar Meqdadi Department of Computer Science and Software Engineering University of Wisconsin-Platteville
Network Layer4-2 Chapter 4: Network Layer Chapter goals: understand principles behind network layer services: network layer service models forwarding versus routing routing (path selection) dealing with scale advanced topics: IPv6, mobility instantiation, implementation in the Internet
Network Layer4-3 Chapter 4: Network Layer 4. 1 Introduction 4.2 Virtual circuit and datagram networks 4.4 IP: Internet Protocol Datagram format IPv4 addressing IPv6 4.5 Routing algorithms Link state Distance Vector Hierarchical routing 4.6 Routing in the Internet RIP OSPF BGP 4.7 Broadcast and multicast routing
Network Layer4-4 Network layer transport segment from sending to receiving host on sending side encapsulates segments into datagrams on rcving side, delivers segments to transport layer network layer protocols in every host, router router examines header fields in all IP datagrams passing through it application transport network data link physical application transport network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical
Network Layer4-5 Two Key Network-Layer Functions forwarding: move packets from router’s input to appropriate router output routing: determine route taken by packets from source to dest. routing algorithms analogy: r routing: process of planning trip from source to dest r forwarding: process of getting through single interchange
Network Layer value in arriving packet’s header routing algorithm local forwarding table header value output link Interplay between routing and forwarding
Network Layer4-7 Connection setup 3 rd important function in some network architectures: ATM, frame relay, X.25 before datagrams flow, two end hosts and intervening routers establish virtual connection routers get involved network vs transport layer connection service: network: between two hosts (may also involve intervening routers in case of VCs) transport: between two processes
Network Layer4-8 Chapter 4: Network Layer 4. 1 Introduction 4.2 Virtual circuit and datagram networks 4.4 IP: Internet Protocol Datagram format IPv4 addressing ICMP IPv6 4.5 Routing algorithms Link state Distance Vector Hierarchical routing 4.6 Routing in the Internet RIP OSPF BGP 4.7 Broadcast and multicast routing
Network Layer4-9 Network layer connection and connection-less service datagram network provides network-layer connectionless service VC network provides network-layer connection service analogous to the transport-layer services, but: service: host-to-host no choice: network provides one or the other implementation: in network core
Network Layer4-10 Virtual circuits call setup, teardown for each call before data can flow each packet carries VC identifier (not destination host address) every router on source-dest path maintains “state” for each passing connection link, router resources (bandwidth, buffers) may be allocated to VC (dedicated resources = predictable service) “source-to-dest path behaves much like telephone circuit” performance-wise
Network Layer4-11 VC implementation a VC consists of: 1. path from source to destination 2. VC numbers, one number for each link along path 3. entries in forwarding tables in routers along path packet belonging to VC carries VC number (rather than dest address) VC number can be changed on each link. New VC number comes from forwarding table
Network Layer4-12 Forwarding table VC number interface number Incoming interface Incoming VC # Outgoing interface Outgoing VC # … … Forwarding table in northwest router: Routers maintain connection state information!
Network Layer4-13 Datagram networks no call setup at network layer routers: no state about end-to-end connections no network-level concept of “connection” packets forwarded using destination host address packets between same source-dest pair may take different paths application transport network data link physical application transport network data link physical 1. Send data 2. Receive data
Network Layer4-14 Forwarding table Destination Address Range Link Interface through through through otherwise 3 4 billion possible entries
Network Layer4-15 Longest prefix matching Prefix Match Link Interface otherwise 3 DA: Examples DA: Which interface?
Network Layer4-16 Datagram or VC network: why? Datagram (Internet) data exchange among computers “elastic” service, no strict timing req. “smart” end systems (computers) can adapt, perform control, error recovery simple inside network, complexity at “edge” many link types different characteristics uniform service difficult VC (ATM) evolved from telephony human conversation: strict timing, reliability requirements need for guaranteed service “dumb” end systems telephones complexity inside network